[teiid-issues] [JBoss JIRA] (TEIID-5969) The "already removed" exception in case of copyLobs=true translator property for MSSQL

[Steven Hawkins (Jira)]

    [ https://issues.redhat.com/browse/TEIID-5969?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14148325#comment-14148325 ] 

Steven Hawkins commented on TEIID-5969:
---------------------------------------

There are a couple of things getting mixed together here.

 

> in the case of MSSQL connector and copyLobs=true in its translator property.

 

That is not expected.  We should create a disk / memory backed copy that will live as long as the query is open.

 

> After debugging I discovered that the error occurred actually because of not enough value in

 

That is not really correlated to copyLobs - it controls how much of a lob we may hold in memory / inline vs. disk.  You may have found a code path though were that is inhibiting the full copying and thus seeing the already removed exception.

 

> But if someone put a data with text field type in MSSQL having more than, say, 20000 symbols then the field won't be read by Teiid at all, Teiid will just throw out the exception mentioned above.

 

Again that is not expected.  What should happen is that the initial copy will happen, then the cast will truncate the lob value.

 

> Will it be possible to improve LobManager so that it can read Text data dynamically increasing needed memory for the process? Otherwise even setting the org.teiid.maxStringLength to 20000 Teiid can raise the exception because of a Text data with length more than 20000 symbols.

 

No, that is really a separate consideration.  You are asking about having dynamic / unlimited length string values by default - that is dangerous from a memory management perspective.

 

 

 

> The "already removed" exception in case of copyLobs=true translator property for MSSQL
> --------------------------------------------------------------------------------------
>
>                 Key: TEIID-5969
>                 URL: https://issues.redhat.com/browse/TEIID-5969
>             Project: Teiid
>          Issue Type: Quality Risk
>          Components: Query Engine
>    Affects Versions: 13.1
>            Reporter: Dmitrii Pogorelov
>            Assignee: Steven Hawkins
>            Priority: Major
>
> We're getting the following exception:
> {code:java}
> 2020-06-10 16:01:45,326 WARN  [org.teiid.PROCESSOR] (Worker21_QueryProcessorQueue272) 1bxj3NJqJLpO TEIID30020 Processing exception for request 1bxj3NJqJLpO.10 'TEIID30328 Unable to evaluate convert(ms_dwh.v1.expr1, string): TEIID30384 Error while evaluating function convert'. Originally ExpressionEvaluationException 'already removed' FileStore.java:156. Enable more detailed logging to see the entire stacktrace. {code}
> in the case of MSSQL connector and copyLobs=true in its translator property.
> After debugging I discovered that the error occurred actually because of not enough value in
> MAX_LOB_MEMORY_BYTES which is used in LobManager. The variable depends on 
> org.teiid.maxStringLength which is set usually to 4000 by default. But if someone put a data with text field type in MSSQL having more than, say, 20000 symbols then the field won't be read by Teiid at all, Teiid will just throw out the exception mentioned above. Will it be possible to improve LobManager so that it can read Text data dynamically increasing needed memory for the process? Otherwise even setting the org.teiid.maxStringLength to 20000 Teiid can raise the exception because of a Text data with length more than 20000 symbols.
>  
> Steps to reproduce:
>  # create the v1 table in MSSQL:
> {code:java}
> CREATE TABLE [dbo].[v1](CREATE TABLE [dbo].[v1]( [expr1] [text] NULL, [b] [int] NULL) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY] {code}
> 2. insert in the table the following data (I did it via standard MSSQL Server Management Studio):
> {code:java}
> insert into test_dwh.dbo.v1 values (replicate(convert(varchar(max),'a'), 20000), 1) ; {code}
> 3. add MSSQL as a source to Teiid:
> {code:java}
>                 <datasource jndi-name="java:/mssql-test-dwh" pool-name="mssql-test-dwh" enabled="true" use-java-context="true">
>                     <connection-url>jdbc:sqlserver://localhost:1433;databaseName=test_dwh</connection-url>
>                     <driver-class&amp;gt;com.microsoft.sqlserver.jdbc.SQLServerDriver</driver-class&amp;gt;
>                     <driver>com.microsoft.sqlserver</driver>
>                     <new-connection-sql>SET ANSI_WARNINGS OFF</new-connection-sql>
>                     <pool>
>                         <min-pool-size>2</min-pool-size>
>                         <max-pool-size>70</max-pool-size>
>                     </pool>
>                     <security>
>                         <user-name>*****</user-name>
>                         <password>*****</password>
>                     </security>
>                     <validation>
>                         <check-valid-connection-sql>select 1</check-valid-connection-sql>
>                     </validation>
>                     <timeout>
>                         <blocking-timeout-millis>120000</blocking-timeout-millis>
>                         <idle-timeout-minutes>5</idle-timeout-minutes>
>                     </timeout>
>                 </datasource>{code}
> 4. add ms model:
> {code:java}
> <model name="ms_dwh">
>         <property name="importer.useFullSchemaName" value="false"/>
>         <property name="importer.tableTypes" value="TABLE,VIEW"/>
>         <property name="importer.importKeys" value="false"/>
>         <property name="importer.schemaPattern" value="dbo"/>
>         <source name="dwh_ms" translator-name="mySqlserver" connection-jndi-name="java:/mssql-test-dwh"/>
>     </model>{code}
> 5. add mySqlserver translator:
> {code:java}
> <translator name="mySqlserver" type="sqlserver">
>         <property name="SupportsNativeQueries" value="true"/>
>         <property name="copyLobs" value="true"/>
>     </translator> {code}
> 6. try to run the following query:
> {code:java}
> select cast(expr1 as string) from ms_dwh.v1 ;; {code}



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